This invention relates to a power control device for hot gas engines of the type adapted to maintain a predetermined engine speed regardless of the power output and in which the power output is controlled by varying the amount of working gas in the engine, said device comprising a generator, an electronic unit providing an output signal in dependence of the difference between the desired and the actual engine speed, solenoid valves governing the amount of working gas in the engine, and a compressor and a reservoir for working gas. A power control device of this type has been described e.g. in the U.S. Pat. No. 3,999,388.
In principle such device operates the way that in case of need for more power a solenoid valve opens a conduit from the reservoir to the working gas spaces of the engine. In case of reduced need for power a connection from the pressure side of the compressor to the reservoir is opened while a check valve ensures that the flow of gas only can be effected in this direction. In case the load on the engine should cease completely the working gas spaces of the engine are short circuited causing the power output to stop.
In the known power control system a greater number of solenoid valves, check valves and gas conduits are used. The object of the present invention is to provide a simpler, cheaper and more reliable system which consumes less power.